Flat STI surface for gate oxide uniformity in Fin FET devices

ABSTRACT

Operations in fabricating a Fin FET include providing a substrate having a fin structure, where an upper portion of the fin structure has a first fin surface profile. An isolation region is formed on the substrate and in contact with the fin structure. A portion of the isolation region is recessed by an etch process to form a recessed portion and to expose the upper portion of the fin structure, where the recessed portion has a first isolation surface profile. A thermal hydrogen treatment is applied to the fin structure and the recessed portion. A gate dielectric layer is formed with a substantially uniform thickness over the fin structure, where the recessed portion is adjusted from the first isolation surface profile to a second isolation surface profile and the fin structure is adjusted from the first fin surface profile to a second fin surface profile by the thermal hydrogen treatment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application62/211,682 filed Aug. 28, 2015, the subject matter of which isincorporated herein by reference in entirety.

BACKGROUND

With increasing down-scaling of integrated circuits and increasinglydemanding requirements to speed of integrated circuits, transistors needto have higher drive currents with increasingly smaller dimensions. FinField-Effect Transistors (Fin FET) were thus developed. Fin FETs includevertical semiconductor fins above a substrate. The semiconductor finsare used to form source and drain regions, and channel regions betweenthe source and drain regions. Shallow Trench Isolation (STI) regions areformed to define the semiconductor fins. The Fin FETs also include gatestacks, which are formed with sidewalls and over the top surfaces of thesemiconductor fins.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It is tobe understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of thepresent disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. It is notedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is an exemplary perspective view of a Fin Field-Effect Transistor(Fin FET) device in accordance with some embodiments of the presentdisclosure.

FIGS. 2A and 2B are exemplary cross sectional views of the Fin FETdevice having a fin structure along a gate electrode in accordance withsome embodiments of the present disclosure.

FIGS. 3-11 illustrate examples of cross-sectional views of intermediatestages of a sequential fabrication process of a Fin FET structure inaccordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.”

FIG. 1 is an exemplary perspective view of a Fin Field-Effect Transistor(Fin FET) device 100 having a fin structure according to one embodimentof the present disclosure, and FIG. 2A is an exemplary cross sectionalview of the Fin FET device 100 having a fin structure along a gateelectrode according to one embodiment of the present disclosure. Inthese figures, some layers/features are omitted for simplification. FIG.2B is a detailed view of a single fin in FIG. 2A.

The Fin FET device 100 depicted in FIGS. 1, 2A, and 2B includes, amongother features, a substrate 110, a fin structure 120, a gate dielectriclayer 130 and a gate electrode layer 140. In this embodiment, thesubstrate 110 is a silicon substrate. Alternatively, the substrate 110may comprise another elementary semiconductor, such as germanium; acompound semiconductor including IV-IV compound semiconductors such asSiC and SiGe, III-V compound semiconductors such as GaAs, GaP, GaN, InP,InAs, InSb, GaAsP, AlGaN, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP;or combinations thereof. In one embodiment, the substrate 110 is asilicon layer of an SOI (silicon-on insulator) substrate. When an SOIsubstrate is used, the fin structure 120 may protrude from the siliconlayer of the SOI substrate or may protrude from the insulator layer ofthe SOI substrate. In the latter case, the silicon layer of the SOIsubstrate is used to form the fin structure 120. Amorphous substrates,such as amorphous Si or amorphous SiC, or insulating material, such assilicon oxide may also be used as the substrate 110. The substrate 110may include various regions that have been suitably doped withimpurities (e.g., p-type or n-type conductivity).

The fin structure 120 is disposed over the substrate 110. The finstructure 120 may be made of the same material as the substrate 110 andmay continuously extend from the substrate 110. In this embodiment, thefin structure 120 is made of silicon (Si). The silicon layer of the finstructure 120 may be intrinsic, or appropriately doped with an n-typeimpurity or a p-type impurity.

In FIG. 1, one fin structure 120 is disposed over the substrate 110,while in FIG. 2A, three fin structures 120 are disposed over thesubstrate 110. However, the number of the fin structures is not limitedto one or three. The numbers may be two or four or more. In addition,one or more dummy fin structures may be disposed in contact with bothsides of the fin structures 120 to improve pattern fidelity inpatterning processes. The width of the fin structure 120 is in a rangeof about 5 nm to about 40 nm in some embodiments, and may be in a rangeof about 7 nm to about 12 nm in certain embodiments. The height of thefin structure 120 is in a range of about 100 nm to about 300 nm in someembodiments, and may be in a range of about 50 nm to 100 nm in otherembodiments.

In FIG. 2, spaces between the fin structures 120 and/or a space betweenone fin structure and another element formed over the substrate 110 arefilled by an isolation insulating layer (e.g., isolation region 150)including one or more layers of insulating materials. The insulatingmaterials for the isolation region 150 may include one or more layers ofsilicon oxide, silicon nitride, silicon oxynitride (SiON), SiOCN,fluorine-doped silicate glass (FSG), or a low-k dielectric material.

The lower part of the fin structure 120 under the gate electrode layer140 is referred to as a well region 120A, and the upper part of the finstructure 120 is referred to as a channel region 120B, as shown in FIG.2A. Under the gate electrode layer 140, the well region 120A is embeddedin the isolation region 150, and the channel region 120B protrudes fromthe isolation region 150. A lower part of the channel region 120B mayalso be embedded in the isolation region 150 to a depth of about 1 nm toabout 5 nm. Although the upper corners of the fin structures 120 shownin FIG. 2 have right angles, this is only for an illustration purpose,and the shape of the upper corners of the fin structures 120 will bedescribed later.

The channel region 120B protruding from the isolation region 150 iscovered by a gate dielectric layer 130, and the gate dielectric layer130 is further covered by a gate electrode layer 140. Part of thechannel region 120B not covered by the gate electrode layer 140functions as a source and/or drain of the Fin FET device 100 (see, FIG.1).

In certain embodiments, the gate dielectric layer 130 includes a singlelayer or alternatively a multi-layer structure, having one or moredielectric materials, such as a single layer of silicon oxide, siliconnitride, or high-k dielectric material, other suitable dielectricmaterial, and/or combinations thereof, or a multilayer of two or more ofthese materials. Examples of high-k dielectric material include HfO₂,HfSiO, HfSiON, HMO, HfTiO, HfZrO, zirconium oxide, aluminum oxide,titanium oxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, othersuitable high-k dielectric materials, and/or combinations thereof.

The gate electrode layer 140 includes one or more layers of any suitablematerial, such as polysilicon, aluminum, copper, titanium, tantalum,tungsten, cobalt, molybdenum, tantalum nitride, nickel silicide, cobaltsilicide, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metal alloys, othersuitable materials, and/or combinations thereof. The gate structure maybe formed using a gate-last or replacement gate methodology.

In certain embodiments of the present disclosure, one or more workfunction adjustment layers 160 may be interposed between the gatedielectric layer 130 and the gate electrode layer 140. The work functionadjustment layer 160 may include a single layer or alternatively amulti-layer structure, such as various combinations of a metal layerwith a selected work function to enhance the device performance (workfunction metal layer), liner layer, wetting layer, adhesion layer, metalalloy or metal silicide. The work function adjustment layers 160 aremade of one or more conductive materials such as a single layer of Ti,Ag, Al, TiAIN, TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru, Mo, Al, WN, Cu,W, Re, Ir, Co, Ni, other suitable metal materials, or a multilayer oftwo or more of these materials. In some embodiments, the work functionadjustment layer 160 may include a first metal material for then-channel Fin FET and a second metal material for the p-channel Fin FET.For example, the first metal material for the n-channel Fin FET mayinclude metals having a work function substantially aligned with a workfunction of the substrate conduction band, or at least substantiallyaligned with a work function of the conduction band of the channelregion 120B. Similarly, for example, the second metal material for thep-channel Fin FET may include metals having a work functionsubstantially aligned with a work function of the substrate valenceband, or at least substantially aligned with a work function of thevalence band of the channel region 120B. In some embodiments, the workfunction adjustment layer 160 may alternatively include a polysiliconlayer. The work function adjustment layer 160 may be formed by ALD, PVD,CVD, e-beam evaporation, or other suitable process. Further, the workfunction adjustment layer 160 may be formed separately for the n-channelFin FET and the p-channel Fin FET which may use different metal layers.

Source and drain regions 125 are also formed in the upper part of thefin structure 120 not covered by the gate electrode layer 140, byappropriately doping impurities in the source and drain regions 125. Analloy of Si or Ge and a metal such as Co, Ni, W, Ti or Ta may be formedon the source and drain regions 125.

In the formation of the isolation region 150, etching operations areperformed to recess a top surface 117 of the isolation region 150 toexpose part of the fin structures 120. As a result of the etchingoperation, in particular a wet etching process, a center portion of thetop surface 117 between the fin structures 120 appears lower than theedges of the top surface 117, which is adjacent to sidewalls 124 of thefin structures 120, such that the top surface 117 has curved edges 117 awith a flat center. The curved edges 117 a are residual portions ofisolation region 150 because the etching is not ideal, as shown in FIG.2B. The residual portions of the isolation region 150 inhibit subsequentgate dielectric growth at the curved edges 117 a, resulting in a thinnergate oxide at these portions, which impacts the breakdown voltage of theFin FET device 100 and leads to larger leakage currents across the gatethinned gate dielectric layer 130 at these portions.

Furthermore, the curved edge surface profile of the isolation region 150may reduce the effective area of the channel region. In addition, theshape of the upper corners of the fin structures may affect theformation of the gate dielectric layer and the device performance. Forexample, as shown in FIG. 2B, when the fin structure has a sharp corner,such as when the upper edge 123 is substantially perpendicular to thesidewalls 124, the gate dielectric layer 130 at the top corners of thefin structure 120 is thinner than other portions of the gate dielectriclayer due to a Si orientation effect. The thinner portions of the gatedielectric layer 130 a may induce yield loss from plasma-induced damage.

The present disclosure provides a method of fabricating the Fin FETdevice 100 using a thermal hydrogen treatment operation after theformation of the isolation region 150 in the Fin FET device 100 suchthat the effects from the curved edge surface profile are decreasedthereby improving performance of the Fin FET device 100 (see, FIG. 8A).For example, physical dimensions of edge portions 718 of the top surface717 of the isolation region 150 can be decreased to minimize the curvededge surface profile. Such minimization of the curved edge surfaceprofile increases an effective area of the channel region and reducesthinning of the gate dielectric layer 130 at the fin structure 100corners and facilitates gate oxide thickness conformity in the gatedielectric layer 130. In addition, the thermal hydrogen treatment causesthe top corners of the fin structure 120 to become substantially rounded(see, FIGS. 8A and 8B), which further facilitates the gate oxidethickness conformity thereby improving the breakdown voltage andminimizing the leakage current in the Fin FET device 100.

FIGS. 3-11 illustrate examples of cross-sectional views of intermediatestages of a sequential fabrication process of a Fin FET device 100 inaccordance with some embodiments of the present disclosure. It isunderstood that additional operations can be provided before, during,and after operations shown by FIGS. 3-11, and some of the operationsdescribed below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations may beinterchangeable. The cross-sectional views in FIGS. 3-9 are taken undera gate, and the cross-sectional views in FIGS. 10 and 11 are taken at asource/drain region.

FIG. 3 is a cross-sectional view of the Fin FET device 100 at a stage offabrication according to an embodiment of the present disclosure. Inthis embodiment, the Fin FET device 100 includes a substrate 110. In oneembodiment, the substrate 110 includes a crystalline silicon substrate(e.g., wafer). A p-type substrate or n-type substrate may be used andthe substrate 110 may include various doped regions, depending on designrequirements. In some embodiments, the doped regions is doped withp-type or n-type dopants. For example, the doped regions may be dopedwith p-type dopants, such as boron; n-type dopants, such as phosphorusor arsenic; and/or combinations thereof. The doped regions may beconfigured for an n-type Fin FET, or alternatively configured for ap-type Fin FET.

In some alternative embodiments, the substrate 110 is made of some othersuitable elemental semiconductor, such as diamond or germanium; asuitable compound semiconductor, such as gallium arsenide, siliconcarbide, indium arsenide, or indium phosphide; or a suitable alloysemiconductor, such as silicon germanium carbide, gallium arsenicphosphide, or gallium indium phosphide. Also alternatively, thesubstrate may include an epitaxial layer. For example, the substrate mayhave an epitaxial layer overlying a bulk semiconductor. Further, thesubstrate may be strained for performance enhancement. For example, theepitaxial layer may include a semiconductor material different from thatof the bulk semiconductor, such as a layer of silicon germaniumoverlying bulk silicon or a layer of silicon overlying bulk silicongermanium. Such strained substrates may be formed by selective epitaxialgrowth (SEG). Furthermore, the substrate may include an SOI structure.Also alternatively, the substrate may include a buried dielectric layer,such as a buried oxide (BOX) layer, such as that formed by separation byimplantation of oxygen (SIMOX) technology, wafer bonding, SEG, or otherappropriate process.

In one embodiment, a pad layer 304 a and a mask layer 304 b are formedon the semiconductor substrate 110. The pad layer 304 a may be a thinfilm having silicon oxide formed, for example, using a thermal oxidationprocess. The pad layer 304 a may act as an adhesion layer between thesemiconductor substrate 110 and the mask layer 304 b. The pad layer 304a may also act as an etch stop layer for etching the mask layer 304 b.In at least one embodiment, the mask layer 304 b is formed of siliconnitride, for example, using low-pressure chemical vapor deposition(LPCVD) or plasma enhanced chemical vapor deposition (PECVD). The masklayer 304 b is used as a hard mask during subsequent patterningprocesses. A photoresist layer 306 is formed on the mask layer 304 b andis then patterned by a photolithography patterning process. Thephotoresist layer may be removed after patterning of the mask layer 304b and pad layer 304 a and before the trench etching.

FIG. 4 is a cross-sectional view of the Fin FET device 100 at one stageof the sequential fabrication process according to an embodiment of thepresent disclosure. The mask layer 304 b and pad layer 304 a are etchedto expose underlying semiconductor substrate 110. The exposedsemiconductor substrate 110 is then trench-etched to form trenches 402by using the patterned mask layer 304 b and pad layer 304 a as a mask.

In the trench etching process, the substrate 110 may be etched byvarious methods, including a dry etch, a wet etch, or a combination ofdry etch and wet etch. The dry etching process may implementfluorine-containing gas (e.g., CF₄, SF₆, CH₂F₂, CHF₃, and/or C₄F₈),chlorine-containing gas (e.g., Cl₂, CHCl₃, CCl₄, and/or BCl₃),bromine-containing gas (e.g., HBr and/or CHBr₃), oxygen-containing gas,iodine-containing gas, other suitable gases and/or plasmas, orcombinations thereof.

Next, a wet etching operation may be performed to remove a native oxideof the semiconductor substrate 110. The wet etching operation may beperformed using dilute hydrofluoric (DHF) acid. Portions of thesemiconductor substrate 110 between trenches 402 form semiconductor fins120. The fins 120 may be arranged in strips (viewed from in the top ofthe Fin FET device 100) parallel to each other, and closely spaced withrespect to each other. Each of the fins 120 has a width W and a heightH, and are spaced apart from an adjacent fin by a width S of the trench402. For example, the width W of the semiconductor fin 120 may be in arange of about 3 nm to about 30 nm in some embodiments.

FIG. 5 is a cross-sectional view of the Fin FET device 100 at one stageof the sequential fabrication process according to an embodiment of thepresent disclosure. Trenches 402 are filled with a dielectric material502. The dielectric material 502 may include a single layer or amultilayered structure having one or more dielectric materials, such asa single layer of silicon oxide, silicon nitride, or high-k dielectricmaterial, other suitable dielectric material, and/or combinationsthereof, or a multilayer of two or more of these materials. In one ormore implementations, the dielectric material 502 is made of, forexample, silicon dioxide formed by LPCVD (low pressure chemical vapordeposition), plasma-CVD or flowable CVD. In the flowable CVD, flowabledielectric materials instead of silicon oxide are deposited. Flowabledielectric materials, as their name suggests, can “flow” duringdeposition to fill gaps or spaces with a high aspect ratio. Usually,various chemistries are added to silicon-containing precursors to allowthe deposited film to flow. In some embodiments, nitrogen hydride bondsare added. Examples of flowable dielectric precursors, particularlyflowable silicon oxide precursors, include a silicate, a siloxane, amethyl silsesquioxane (MSQ), a hydrogen silsesquioxane (HSQ), anMSQ/HSQ, a perhydrosilazane (TCPS), a perhydro-polysilazane (PSZ), atetraethyl orthosilicate (TEOS), or a silyl-amine, such as trisilylamine(TSA). These flowable silicon oxide materials are formed in amultiple-operation process. After the flowable film is deposited, it iscured and then annealed to remove un-desired elements to form siliconoxide. When the un-desired elements are removed, the flowable filmdensities and shrinks. In some embodiments, multiple anneal processesare conducted. The flowable film is cured and annealed.

In some embodiments, other dielectric materials, such as siliconnitride, silicon oxynitride, fluorine-doped silicate glass (FSG), or alow-k dielectric material, are also used to form the dielectric material502. In an embodiment, the dielectric material 502 is formed using ahigh-density-plasma (HDP) CVD process, using silane (SiH₄) and oxygen(O₂) as reacting precursors. In other embodiments, the dielectricmaterial 502 may be formed using a sub-atmospheric CVD (SACVD) processor high aspect-ratio process (HARP), in which process gases may includetetraethylorthosilicate (TEOS) and/or ozone (O₃). In yet otherembodiments, the dielectric material 502 may be formed using aspin-on-dielectric (SOD) process, such as hydrogen silsesquioxane (HSQ)or methyl silsesquioxane (MSQ). In some embodiments, the filled recessregion (or the trenches 402) may have a multi-layer structure such as athermal oxide liner layer filled with silicon nitride or silicon oxide.

FIG. 6 is a cross-sectional view of the Fin FET device 100 at one ofvarious stages of the sequential fabrication process according to anembodiment of the present disclosure. After the deposition of thedielectric material 502, planarization operations such as a chemicalmechanical polish (CMP) and/or an etch-back process are then performed,followed by the removal of the mask layer 304 b and pad layer 304 a. Anannealing process may be performed after the planarization operations.The annealing process includes rapid thermal annealing (RTA), laserannealing processes, or other suitable annealing processes.

In at least one embodiment, the mask layer 304 b is formed of siliconnitride such that the mask layer 304 b may be removed using a wetprocess using H₃PO₄. The pad layer 304 a may be removed using dilute HFacid if the pad layer 304 a is formed of silicon oxide. The remainingportions of the dielectric material 502 in the trenches 402 arehereinafter referred to as isolation regions 150. In some embodiments,the removal of the mask layer 304 b and the pad layer 304 a is performedafter the recessing of the isolation regions 150, which recessingoperation is shown in FIG. 7.

FIG. 7 is a cross-sectional view of the Fin FET device 100 at one stageof the sequential fabrication process according to an embodiment of thepresent disclosure. An etching process may be performed to etchisolation regions 150 to expose upper portions 722 of the semiconductorfins 120 from the isolation regions 150. The etching process may includea dry etching process, wet etching process, or a combination of dry andwet etching processes to remove portions of the isolation regions 150.It is understood that the etching process may be performed as oneetching process or multiple etching processes.

The remaining isolation regions 150 include top surfaces 717. Further,the upper portions 722 of the semiconductor fins 120 protruding over thetop surfaces 717 of the remaining isolation regions 150 thus are used toform part of an active area, such as a channel region, of the Fin FETdevice 100. The upper portions 722 of the semiconductor fins 120 mayinclude top surfaces 723 and sidewalls 724. Height H1 of the upperportions 722 of the semiconductor fins 120, which is to be a channelregion, from the top surface 717 of the isolation regions 150 may be ina range of about 6 nm to about 100 nm. In some embodiments, the heightH1 is greater than 100 nm or smaller than 6 nm.

As shown in FIG. 7, curved edge surface isolation regions 718 may bepresent at the top surfaces 717 of the isolation regions 150 sandwichedby two fins 120. In the present disclosure, the curved edge surfaceisolation structures are defined by curved edges abutting the sidewalls724 of the channel region 120B with a flat center on the top surface717. The height ΔH of the curved edge surface isolation structures 718are in a range of 0.3H1<ΔH<0.5H1 in some embodiments, and in a range of0.5H1<ΔH<0.7H1 in other embodiments.

The curved edge surface isolation regions 718 reduces surface areaavailable in the channel region 120B and causes non-uniform gatedielectric layer at the bottom of the channel region. The decrease inactive surface area caused by the curved edge surface isolationstructures 718 adversely impacts the collection of channel current flow.The non-uniform oxide thickness caused by the thinning effects alsoimpacts the breakdown voltage of the Fin FET device 100 and induces anincrease in leakage current across the gate oxide. The leakage currentcan be observed near the edges of the top surface 723 of the fins 120,where the thickness of the gate oxide is smaller than that of thesidewalls 724 and/or the top surface 723. In many cases, the variationin thickness across the surface of the channel region 120B can vary bymore than 0.6 nm. The thickness of the gate oxide at the edges of thetop surfaces 723 of the semiconductor fins 120 becomes relativelysmaller due to a Si orientation effect. Such thinning gate oxide mayinduce yield loss from plasma-induced damage.

In one or more implementations of the present application, a thermalhydrogen treatment is applied to the fin structure and the recessedoxide portion to improve the shape of the fin structure and tosubstantially eliminate the curved edge surface isolation structures 718at the interface of the fin structure and the recessed oxide portion.

In this embodiment, the thermal hydrogen treatment is applied with ahydrogen content ambient such as a hydrogen gas (H₂). The thermalhydrogen treatment is applied at a gas flow rate in a range of fromabout 0.2 standard-liter-per-minute (slm) to about 50 slm in someembodiments. The thermal hydrogen treatment is applied at a temperaturein a range of from about 700° C. to about 1100° C. in some embodiments,and at a temperature in a range of from about 850° C. to about 1000° C.in other embodiments. The thermal hydrogen treatment is applied at apressure in a range of about 0.2 Torr to about 760 Torr in someembodiments. The thermal hydrogen treatment may be applied for aduration in a range of about 20 seconds to about 120 seconds in someembodiments. In one or more implementations, the thermal hydrogentreatment is applied for a duration of 80 seconds.

The hydrogen gas may be combined with one or more carrier gases, such ashelium, nitrogen, or argon. The concentration of hydrogen in the carriergas ranges from 2% to 80% based on the total number of moles of hydrogenand carrier gas. In certain embodiments, ammonia (NH₃) is used. When NH₃is used, the NH₃ can be dissociated into hydrogen and nitrogen atelevated temperatures in accordance with the reaction: 2NH₃→N₂+3H₂.

FIG. 8A is a cross-sectional view of the Fin FET device 100 at one stageof the sequential fabrication process according to an embodiment of thepresent disclosure. FIG. 8B is a detailed view of a single fin after thegate dielectric layer 130 is formed. After the hydrogen treatment, thecurved edge surface isolation structures can be diminished or eliminatedin some embodiments, as shown in FIG. 8A and the upper corners of thefin structure can be rounded. For example, the semiconductor fins 120are adjusted from a first fin surface profile (e.g., square upper edges)to a second fin surface profile (e.g., substantially round upper edges)based on the thermal hydrogen treatment. As shown in FIGS. 8A and 8B,the radius of the curvature R at the corners of the semiconductor fin120 can be 0.05 W<R<0.5 W in some embodiments, where W is a width of thechannel region of the semiconductor fin 120, or 0.1 W<R<0.2 W in otherembodiments. The change in height of the curved edge surface isolationstructures 718 is in a range of 0.05H1<ΔH′<0.1H1 in some embodiments,and in a range of 0.1H1<ΔH′<0.3H1 in other embodiments, where H1 is theheight of the upper portions 722 of the semiconductor fins 120. Incontrast to the upper edges 723 of the fin structure prior to thethermal hydrogen treatment (see, FIG. 7), the fraction of the width andthe fraction of the height that is curved after the thermal hydrogentreatment is significantly larger. Conversely, the bottom edges at theinterface of the fin structure and recessed oxide portion (see, FIG. 7),the fraction of the height that is curved after the thermal hydrogentreatment is significantly smaller.

The top surface 717 of the isolation region may have a substantiallyflat step height as a result of the thermal hydrogen treatment. Inaddition, the top surface 723 of the semiconductor fin 120 may havesubstantially rounded corners as a result of the applied thermalhydrogen treatment. The substantially flat STI surface provides a largeractive surface area of the channel region and the substantially roundedcorners of the semiconductor fin 120 provides a uniform thickness gatedielectric 130, thereby improving the breakdown voltage and minimizingthe leakage current in the Fin FET device 100.

FIG. 9 is a cross-sectional view of the Fin FET device 100 at one stageof the sequential fabrication process according to an embodiment of thesubject technology. A gate stack 920 is formed over the substrate 110over the top surface 723 and sidewalls 724 of the semiconductor fin 120,and extending to the top surfaces 717 of the first isolation region 150a and the second isolation region 150 b. The gate stack 920 includes agate dielectric layer 130 and a gate electrode layer 140 disposed on thegate dielectric layer 130. During the formation of the gate stack 920,various cleaning/etching processes, which etch the isolation regions150, may be performed.

The gate dielectric 130 is formed to cover the top surface 723 andsidewalls 724 of at least a portion of the channel region of thesemiconductor fins 120. The gate dielectric formed on the upper surfaceof the isolation region is not shown in FIG. 9 for simplification. Sincethe upper corners of the fin structures are rounded by the thermalhydrogen treatment, the gate dielectric layer can have a thickness thatis substantially uniform over the fin structure (no or reduced thinningeffect). The uniformity of the gate dielectric layer 130 is alsofacilitated by the reduced curved edge surface profile of the isolationregions 150 at the bottom of the channel region (e.g., removed portionsof the curved edge surface isolation structures 718).

The gate dielectric layer 130 has a thickness in a range of about 1.8nanometers (nm) to about 5 nm in some embodiments, and a thickness in arange of about 2.0 nm to about 4.4 nm in other embodiments. Thethickness of the gate dielectric layer 130 may be in a range of 3 nm to5 nm in certain embodiments. In one or more implementations, the gatedielectric layer 130 has a first thickness t₁ at the top surface 717 ofthe isolation region 150, a second thickness t₂ at the top surface 723of the semiconductor fin 120, and a third thickness t₃ at one or moresidewalls 724 of the semiconductor fin 120. If the gate dielectric layer130 was formed on the structure shown in FIG. 7 without performing thethermal hydrogen treatment, the variation in thickness across thesurface of the channel region 120B would be more than 0.6 nm. Incontrast, by adding the thermal hydrogen treatment, the variations offirst thickness t₁, the second thickness t₂ and the third thickness t₃can be less than 0.3 nm. The variation of the thicknesses at the threeidentified locations may be less than 0.6 nm in other embodiments. Theuniform thickness of the gate dielectric layer 130 can minimize theyield loss from plasma induced damage. Eliminating thinned portions ofthe gate dielectric layer 130 can reduce the leakage current at thethinned portions of the gate dielectric layer 130.

In some embodiments, the gate dielectric layer 130 includes one or morelayers of silicon oxide, silicon nitride, silicon oxy-nitride, or high-kdielectrics. High-k dielectrics may include metal oxides. Examples ofmetal oxides used for high-k dielectrics include oxides of Li, Be, Mg,Ca, Sr, Sc, Y, Zr, Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu, and/or mixtures thereof. The gate dielectric layer 130 maybe formed using a suitable process such as atomic layer deposition(ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD),thermal oxidation, UV-ozone oxidation, or combinations thereof. The gatedielectric layer 130 may include a single layer or multilayer structure.For example, the gate dielectric layer 130 may further include aninterfacial layer (not shown) to reduce damage between the gatedielectric layer 130 and the fin 120. The interfacial layer may includesilicon oxide.

The gate electrode layer 140 is then formed on the gate dielectric layer130. In at least one embodiment, the gate electrode layer 140 covers theupper portion 722 of more than one semiconductor fin 120, so that theresulting Fin FET device 100 includes more than one fin structure. Insome alternative embodiments, each of the upper portions 722 of thesemiconductor fins 120 may be used to form a separate Fin FET device100. The gate electrode layer 140 may include a single layer or amultilayer structure. The gate electrode layer 140 may includepoly-silicon. Further, the gate electrode layer 140 may be dopedpoly-silicon with uniform or non-uniform doping. In some alternativeembodiments, the gate electrode layer 140 includes a metal such as Al,Cu, W, Ti, Ta, TiN, TiAl, TiAlN, TaN, NiSi, CoSi, other conductivematerials with a work function compatible with the substrate material,or combinations thereof. The gate electrode layer 140 may be formedusing a suitable process such as ALD, CVD, PVD, plating, or combinationsthereof.

FIG. 10 is a cross-sectional view of the Fin FET device 100 at one stageof the sequential fabrication process according to an embodiment of thepresent disclosure. In this example, the cross-sectional view of the FinFET device 100 is taken along an axis outside of the gate stack 920.

The portion of the semiconductor fin 120 not covered by the gateelectrode layer 140 is recessed to form a recessed portion 1026 of thesemiconductor fin 120 having a top surface 1019 below the flat topsurfaces 717 of the isolation regions 150. In one embodiment, a biasedetching process is performed to recess the top surface 1019 of thechannel region that is unprotected or exposed to form the recessedportion 1026 of the semiconductor fin 120. In an embodiment, the etchingprocess may be performed using HBr and/or Cl₂ as etch gases.

FIG. 11 is a cross-sectional view of the Fin FET device 100 at one stageof the sequential fabrication process according to an embodiment of thepresent disclosure. The structures depicted in FIG. 11 are produced byselectively growing a strained material 1130 over the recessed portion1026 of the semiconductor fin 120 and extending over the top surfaces717 of the isolation regions 150. Since the lattice constant of thestrained material 1130 is different from the channel region of thesemiconductor fin 120, the channel region of the semiconductor fin 120is strained or stressed to enable carrier mobility of the device andenhance the device performance. Although the strained material 1130overlying each fin is connected in FIG. 11, the strained material 1130may be formed separately with respect to each fin.

In at least one embodiment, the strained material 1130, such as siliconcarbon (SiC) and/or silicon phosphide (SiP), is epitaxially grown by aLPCVD process to form the source and drain regions of an n-type Fin FET.In another embodiment, the strained material 1130, such as silicongermanium (SiGe), is epitaxially grown by a LPCVD process to form thesource and drain regions of a p-type Fin FET. The p-type Fin FET and then-type Fin FET are separately formed. In this regard, an n-typeepitaxial region or p-type epitaxial region can be defined usingphotolithography and etching processes. For example, a protective layer,such as a silicon nitride (SiN) layer, is formed to cover the p-typeepitaxial region when the n-type epitaxial region is processed (e.g.,S/D formation). Conversely, the SiN layer can cover the n-type epitaxialregion when the p-type epitaxial region is processed.

The Fin FET device 100 serves only as one example. The Fin FET device100 may be used in various applications such as a digital circuit,imaging sensor devices, a hetero-semiconductor device, dynamic randomaccess memory (DRAM) cell, a single electron transistor (SET), and/orother microelectronic devices (collectively referred to herein asmicroelectronic devices). Of course, aspects of the present disclosureare also applicable and/or readily adaptable to other type oftransistor, including single-gate transistors, double-gate transistors,and other multiple-gate transistors, and may be employed in manydifferent applications, including sensor cells, memory cells, logiccells, and others.

The present disclosure provides a method of fabricating a Fin FET device100 using a thermal hydrogen treatment operation after the formation ofthe isolation region 150 in the Fin FET device 100 such that the effectsfrom the curved edge surface profile are decreased, thereby improvingperformance of the Fin FET device 100. For example, physical dimensionsof edge portions at the top surface of the isolation region 150 can bedecreased to minimize the curved edge surface profile. Such minimizationof the curved edge surface profile increases active surface area of thechannel region and facilitates gate dielectric thickness conformity atthe bottom of the channel region by preventing thinning of the gatedielectric layer 130. In addition, the thermal hydrogen treatment causesthe top corners of the fin structure 120 to become substantiallyrounded, which further facilitates the gate oxide thickness conformitythereby improving the breakdown voltage and minimizing the leakagecurrent in the Fin FET device 100.

In an embodiment, a method of fabricating a Fin FET device is describedherein. The method includes providing a substrate having a finstructure, an upper portion of the fin structure having a first finsurface profile. The method also includes forming an isolation region onthe substrate and in contact with the fin structure. The method alsoincludes recessing at least a portion of the isolation region by an etchprocess to form a recessed portion and to expose the upper portion ofthe fin structure, the recessed portion having a first isolation surfaceprofile. The method also includes applying a thermal hydrogen treatmentto the fin structure and the recessed portion. The method furtherincludes forming a gate dielectric layer with a substantially uniformthickness over the fin structure, in which the recessed portion isadjusted from the first isolation surface profile to a second isolationsurface profile and the fin structure is adjusted from the first finsurface profile to a second fin surface profile, by the thermal hydrogentreatment.

In another embodiment, a method of fabricating a Fin FET device isdescribed herein. The method includes providing a substrate having finstructures, an upper portion of each of the fin structures having afirst fin surface profile. The method also includes forming an isolationregion on the substrate such that the fin structures are embedded in theisolation region. The method also includes recessing at least a portionof the isolation region by an etch process to form a recessed portionand to expose upper portions of the fin structures, the recessed portionhaving a first isolation surface profile between adjacent two finstructures. The method also includes applying a thermal hydrogentreatment to the fin structures and the recessed portion. The methodfurther includes forming a gate dielectric layer with a substantiallyuniform thickness over the exposed upper portions of fin structures, inwhich the recessed portion is adjusted from the first isolation surfaceprofile to a second isolation surface profile and the upper portions ofthe fin structures are adjusted from the first fin surface profile to asecond fin surface profile, by the thermal hydrogen treatment.

In yet another embodiment, a semiconductor device includes a substrateand a fin structure having a top surface with substantially roundedcorners, the substantially rounded corners being defined by a firstradius of curvature relating to a fraction of a width of a channelregion in the fin structure which is curved along the top surface and asecond radius of curvature relating to a fraction of a height of thechannel region which is curved along sidewalls of the fin structure. Thesemiconductor device also includes an isolation region formed over thesubstrate and in contact with at least a sidewall of the fin structure,the isolation region having a top surface with a substantially flat stepheight based on a thermal hydrogen treatment, the substantially flatstep height being defined by a downward slope from the sidewalls of thefin structure toward the top surface of the isolation region whichrelates to a fraction of the height of the channel region. Thesemiconductor device also includes a gate dielectric layer formed incontact with the fin structure and the top surface of the isolationregion, the gate dielectric layer having a thickness that issubstantially uniform over the fin structure and the isolation regionbased on the thermal hydrogen treatment.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of fabricating a fin field-effecttransistor (Fin FET) device, the method comprising: providing asubstrate having a fin structure, an upper portion of the fin structurehaving a first fin surface profile; forming an isolation region on thesubstrate and in contact with the fin structure; recessing at least aportion of the isolation region by an etch process to form a recessedportion and to expose the upper portion of the fin structure, therecessed portion having a first isolation surface profile; applying athermal hydrogen treatment consisting essentially of hydrogen gas to thefin structure and the recessed portion; and forming a gate dielectriclayer with a substantially uniform thickness over the fin structure,wherein the thermal hydrogen treatment provides: the upper portion ofthe fin structure with a second surface profile, the second surfaceprofile including a top surface of the fin structure havingsubstantially rounded corners being defined by a first radius ofcurvature relating to a fraction of a width of a channel region in thefin structure which is curved along the top surface and a second radiusof curvature relating to a fraction of a height of the channel regionwhich is curved along sidewalls of the fin structure; and the isolationregion with a second surface profile having a substantially flat stepheight, the substantially flat step height being defined by a downwardslope from sidewalls of the fin structure toward a top surface of theisolation region which relates to a fraction of the height of thechannel region.
 2. The method of claim 1, wherein applying the thermalhydrogen treatment comprises flowing the hydrogen gas with a gas flowrate in a range of 0.2 standard-liter-per-minute (slm) to 50 slm.
 3. Themethod of claim 1, wherein the thermal hydrogen treatment is appliedwith a temperature in a range of 750 degrees Celsius to 1000 degreesCelsius.
 4. The method of claim 1, wherein the thermal hydrogentreatment is applied with a pressure in a range of 0.2 Torr to 760 Torr.5. The method of claim 1, wherein the thermal hydrogen treatment isapplied for a duration in a range of 20 seconds to 120 seconds.
 6. Themethod of claim 1, wherein: in the forming the gate dielectric layer,the gate dielectric layer is formed to have a first thickness at a topsurface of the recessed portion, a second thickness at a top surface ofthe fin structure, and a third thickness at one or more sidewalls of thefin structure, and the first thickness, the second thickness and thethird thickness vary from one another by less than 0.3 nanometers. 7.The method of claim 1, further comprising: forming a gate structure overat least a portion of the fin structure and over the isolation region;forming a second recessed portion by etching a part of the finstructure; and forming an epitaxial layer in and above the secondrecessed portion.
 8. The method of claim 1, wherein: the first finsurface profile includes square edges at the upper portion of the finstructure, the first isolation surface profile includes substantiallyround edges at an upper portion of the recessed portion, and the secondisolation surface profile includes square edges at the upper portion ofthe recessed portion.
 9. A method of fabricating a fin field-effecttransistor (Fin FET) device, the method comprising: providing asubstrate having fin structures, an upper portion of each of the finstructures having a first fin surface profile; forming an isolationregion on the substrate such that the fin structures are embedded in theisolation region; recessing at least a portion of the isolation regionby an etch process to form a recessed portion and to expose upperportions of the fin structures, the recessed portion having a firstisolation surface profile between adjacent two fin structures; applyinga thermal hydrogen treatment consisting essentially of hydrogen gas tothe fin structures and the recessed portion; and forming a gatedielectric layer with a substantially uniform thickness over the exposedupper portions of fin structures, wherein the recessed portion isadjusted from the first isolation surface profile to a second isolationsurface profile and the upper portions of the fin structures areprovided with a second surface profile including a top surface of thefin structure having corners with a radius of curvature R, where 0.1W<R<0.2 W, where W is a width of a channel region in the fin structure,by the thermal hydrogen treatment.
 10. The method of claim 9, wherein:the first fin surface profile includes square edges at the upper portionof the fin structure, the first isolation surface profile includessubstantially round edges at an upper portion of the recessed portion,and the second isolation surface profile includes square edges at theupper portion of the recessed portion.
 11. The method of claim 10,wherein applying the thermal hydrogen treatment comprises flowing thehydrogen gas with a gas flow rate in a range of 0.2standard-liter-per-minute (slm) to 50 slm.
 12. The method of claim 9,wherein the thermal hydrogen treatment is applied with a temperature ina range of 750 degrees Celsius to 1000 degrees Celsius.
 13. The methodof claim 9, wherein the thermal hydrogen treatment is applied with apressure in a range of 0.2 Torr to 760 Torr.
 14. The method of claim 9,wherein the thermal hydrogen treatment is applied for a duration in arange of 20 seconds to 120 seconds.
 15. The method of claim 9, wherein:in the forming the gate dielectric layer, the gate dielectric layer isformed to have a first thickness at a top surface of the recessedportion, a second thickness at a top surface of the fin structure, and athird thickness at one or more sidewalls of the fin structure, and thefirst thickness, the second thickness and the third thickness vary fromone another by less than 0.3 nanometers.
 16. The method of claim 9,further comprising: forming a gate structure over at least a portion ofthe fin structure and over the isolation region; forming a secondrecessed portion by etching a part of the fin structure; and forming anepitaxial layer in and above the second recessed portion.
 17. Asemiconductor device, comprising: a substrate; a fin structure having atop surface with substantially rounded corners, the substantiallyrounded corners being defined by a first radius of curvature relating toa fraction of a width of a channel region in the fin structure which iscurved along the top surface and a second radius of curvature relatingto a fraction of a height of the channel region which is curved alongsidewalls of the fin structure; an isolation region formed over thesubstrate and in contact with at least a sidewall of the fin structure,the isolation region having a top surface with a substantially flat stepheight based on a thermal hydrogen treatment, the substantially flatstep height being defined by a downward slope from the sidewalls of thefin structure toward the top surface of the isolation region whichrelates to a fraction of the height of the channel region; and a gatedielectric layer formed in contact with the fin structure and the topsurface of the isolation region, the gate dielectric layer having athickness that is substantially uniform over the fin structure and theisolation region based on the thermal hydrogen treatment.
 18. Thesemiconductor device of claim 17, wherein: the gate dielectric layer hasa first thickness at the top surface of the isolation region, the gatedielectric layer has a second thickness at the top surface of the finstructure, the gate dielectric layer has a third thickness at one ormore sidewalls of the fin structure, and the first thickness, the secondthickness and the third thickness vary from one another by less than 0.3nanometers.
 19. The semiconductor device of claim 17, furthercomprising: a gate stack including a gate electrode layer and the gatedielectric layer, the gate stack covering a portion of the finstructure; and a source and a drain, each including a stressor layerdisposed in and over recessed portions formed in the fin structure, thestressor layer applying a stress to a channel region of the finstructure covered by the gate stack.